Deluge
There are several private trackers that are now ratioless and instead rely on seeding time. The rules will often be like this:
You must seed every torrent to 1:1 or seed for 72 hours within 7 days of completion.
This feature would be most useful for individual torrents, or mainly for Label (so we can set rules for different trackers).
The option should be to stop seeding after reaching X ratio (as we currently have) AND/OR stop seeding once seed time has reached X hours.
I'm not sure if this currently is the case but seed time should not increase if torrents are Queued.